The present invention relates to the field of implantable medical devices. More particularly, the present invention relates to cardiac pacing systems that provide a method for using pacing pulses to terminate an atrial fibrillation by inducing a ventricular extra-systole through combipolar pacing.
Tachyarrhythmias are episodes of high-rate cardiac depolarizations. Tachyarrhythmias may occur in one chamber of the heart or may be propagated from one chamber to another. Some tachyarrhythmias are sufficiently high in rate to compromise cardiac output from the chamber(s) affected, leading to loss consciousness or death, in the case of ventricular fibrillation or weakness and dizziness in the case of atrial fibrillation. Atrial fibrillation is often debilitating, due to the loss of atrial cardiac output, and may sometimes lead to ventricular fibrillation.
Generally, fibrillation may be terminated by administering high energy level cardioversion/defibrillation shocks or pulses until the fibrillation is terminated. For example, in the context of implantable anti-arrhythmia devices, these pulses may be applied by means of large surface area electrodes on or in the chamber to be defibrillated. However, the high energy level pulses are often sufficient to cause pain to the patient. Thus, it would be desirable to prevent or decrease the occurrence of atrial fibrillation.
Thus, some exploration has been made in the use of pacing level pulses, which stimulate the cardiac tissue at much lower levels than defibrillation pulses, to terminate atrial fibrillation. Implantable pulse generators (IPGs) that deliver pacing level pulses are well known in the art. These IPGs may deliver pulses to one or more chambers of the heart. However, in many cases, the low level pacing pulses are not sufficient to terminate atrial fibrillation.
Some exploration has also been made into the possibilities of using ventricular extra-systoles (also known as premature ventricular contractions or PVCs) to capture the atrium and terminate atrial fibrillation.
Some IPGs are dual-chamber, having both atrial and ventricular leads, while other IPGs are multiple-chamber, having one or more leads in two or more chambers of the heart. Such dual-chamber or multiple chamber IPGs have one or more unipolar or bipolar leads in the ventricle and one or more unipolar or bipolar leads in the atrium of the right and/or the left side of the heart. Sensing of cardiac activity takes place either between a tip and a ring of one or more electrodes in a given chamber or between the tip of one or more electrodes in a given chamber and the can of the IPG. Another type of sensing, sometimes called as xe2x80x9ccombipolarxe2x80x9d sensing, takes place between the respective tip electrodes of these unipolar or bipolar leads.
The pacing pulses delivered from such dual-chamber leads and multiple-chamber IPGs may be too low in energy to serve as defibrillation pulses.
However, these IPGs may also pace atrial cardiac tissue with the atrial lead and may pace ventricular tissue with the ventricular lead. The leads of a dual-chamber or a multiple-chamber IPG may also pace tissue between the leads and thereby deliver energy to the ventricle to induce a ventricular extra-systole (VES), also called a premature ventricular contraction (PVC). This type of pacing may simultaneously delivery enough energy to the atria to induce atrial depolarization in the same instance as the VES is being induced.
The close coupling of the premature ventricular action induced by the combipolar pulse to the start of an atrial arrhythmia may induce a rise in atrial pressure. This rise further results in a higher wall tension in the atria thus causing an electrical situation whereas the delivery of energy is more likely to capture the highest possible number of atrial cells. Additionally, the pacing pulses that result from such combipolar pacing may have a higher amplitude and/or pulse width than the usual pacing pulses.
Thus, a need exists in the medical arts for use of combipolar pacing of cardiac tissue to induce a ventricular extra-systole in order to simultaneously terminate atrial fibrillation of the cardiac tissue.
Some methods have been proposed in the prior art for administering pacing pulses to cardiac tissue in order to terminate atrial fibrillation.
For example, U.S. Pat. Nos. 5,562,708 and 5,674,251, both to Combs et al., disclose a pacemaker system adapted to deliver pacing pulses in the presence of fibrillation. An extended pulse train is delivered in order to gradually entrain greater portions of heart tissue, until a sufficient percentage of tissue is entrained to interrupt fibrillation.
U.S. Pat. No. 5,683,429 to Mehra discloses a method and apparatus for preventing fibrillation by distributing sense electrodes one or both atrial chambers. The sense electrodes may be used to sense an atrial premature beat and then to distribute a pacing energy pulse burst simultaneously.
The article xe2x80x9cLes stimulateurs cardiaques destinxc3xa9s à traiter les tachycardies paroxystiquesxe2x80x9d (Cardiac stimulators for treating paroxysmal tachycardias)xe2x80x9d in the journal Stimucoeur Medical by J. F. Leclercq et al. discloses the use of a pacemaker stimulating an atria and a ventricle simultaneously to terminate an arrhythmia in the case of drug-resistant paroxysmal reciprocating tachycardia.
Some methods have also been proposed in the prior art for combipolar sensing. For example, U.S. Pat. No. 5,871,507 to Obel, et al. discloses the use of signal morphology analysis to detect signals between unipolar atrial and ventricular leads.
The most pertinent prior art patents and publications known at the present time are shown in the following table:
J. F. Leclercq, et al. (1979) xe2x80x9cLes stimulateurs cardiaques destinxc3xa9s à traiter les tachycardies paroxystiquesxe2x80x9d (Cardiac stimulators for treating paroxysmal tachycardias)xe2x80x9d, Stimucoeur Medical, Volume 7, No.1, pp. 8-15.
The publications listed in Table 1 are hereby incorporated by reference herein, each in its entirety. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the Claims set forth below, at least some of the devices and methods disclosed in the patent of Table 1 may be modified advantageously in accordance with the teachings of the present invention.
The present invention is therefore directed to providing a method and system for terminating atrial fibrillation by inducing a ventricular extra-systole through combipolar pacing. The system of the present invention overcomes at least some of the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of terminating atrial fibrillation by inducing a ventricular extra-systole.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting the pacing of cardiac tissue. Those problems include, without limitation: (a) patients experiencing discomfort while treatment for atrial fibrillation is being administered; (b) atrial fibrillation being terminated using energy pulses which are uncomfortably high or excessive; (c) pacing energy pulses being less effective in the termination of atrial fibrillation than desired; (d) difficulty in administering high energy stimulus pulses to treat atrial fibrillation, and (e) difficulty in providing pacing pulses of sufficient amplitude and pulse width to cause atrial depolarization.
In comparison to known pacing techniques, various embodiments of the present invention provide one or more of the following advantages: (a) the use of pacing energy level pulses, rather than high energy pulse shocks, to treat atrial fibrillation; (b) the ability to create pacing pulses of higher amplitude or pulse width, and (c) fewer patient complaints of discomfort in the treatment of fibrillation.
Some embodiments of the present invention include one or more of the following features: (a) an IPG capable of treating atrial fibrillation by inducing ventricular extra-systole; (b) an IPG capable of delivering pacing energy level pulses of a higher amplitude or pulse width; (c) methods of treating atrial fibrillation with pacing energy level pulses rather than high energy shocks and (d) methods of inducing ventricular extra-systole sufficient to terminate atrial fibrillation without causing distress to the patient.
At least some embodiments of the present invention involve detecting atrial fibrillation in the cardiac tissue. Immediately following detection of atrial fibrillation, an area of the ventricle is simultaneously paced so that at least one pacing pulse is delivered to an area of the ventricle simultaneously from at least one atrial electrode and at least one ventricular electrode. This simultaneous combipolar pacing induces a ventricular extra-systole for the duration in order to terminate the atrial fibrillation. After the duration ends, the occurrence of atrial fibrillation is again measured. If atrial fibrillation is still detected, another combipolar pacing pulse is administered.
The ventricular extra-systole may be sensed. The simultaneous pacing may occur for a duration, which may be determined using any suitable means. The cardiac tissue may also be placed at a regular function once the duration is over. The rates of pacing with the at least one atrial electrode and/or the at least one ventricular electrode may be adjusted. Simultaneous, combipolar pacing of the area of cardiac tissue may be stopped once the ventricular extra-systole has been delivered and redetection of the atrial rhythm shows a regular function.